This invention relates to the nuclear-reactor art and has particular relationship to the reduction or suppression of excessive radioactive emissions into the atmosphere or the environment of a nuclear-reactor plant. In the interest of concreteness this application deals with pressurized water reactors (PWRs). However, to the extent that this invention is applicable to nuclear reactors of other types, such use of this invention is regarded as within the scope thereof.
A nuclear reactor plant includes a nuclear reactor and one or more vapor, usually steam, generators. Water under pressure of about 2250 pounds per square inch is heated by the heat developed by fission in the reactor to about 600.degree. F. and serves as primary liquid in the steam generator, vaporizing the secondary liquid, usually also water, by heat exchange. The vapor drives a main turbine which generates electrical power. The vapor from the turbine is liquefied in a condenser and returned as secondary liquid to the vapor generators. The condenser is cooled by a cooling liquid, usually water, circulated through cooling coils by pumps. The pumps are driven by the electrical power supplied by the main turbine or by off-site power where available.
The primary-liquid and secondary-liquid pipe or conductor in the vapor generators are sealed from each other. However, the primary liquid is at substantially higher pressure than the secondary liquid and leakage of the primary liquid into the secondary liquid may occur. Since the primary liquid includes raioactive materials, it is necessary to provide environmental protection against radioactive emissions from secondary liquid contaminated with radioactive materials.
Nuclear reactor plants provided in accordance with the teachings of the prior art have no facilities for reducing the radioactive emissions from the secondary liquid. It was contemplated that the leakage, which aries by reason of minor structural defects or water chemistry or other causes, is relatively small, less than 0.1 gallon per minute, and that such small leakage would not produce harmful radiation. In such prior-art apparatus a portion of the secondary liquid is conducted with sediment, such as scale produced by corrosion and dissolved matter and the like into a blowdown tank. The liquid in the blowdown tank is discharged into a discharge receiver, usually a river, ocean or lake and the vapor over the liquid in the tank is vented into the atmosphere. This practice may result in excessive, non-permissible radioactive emission.
Non-permissible radioactive emission also results when a major failure occurs in the apparatus. Typical of a major failure are rupture of the primary conductors (steam generator tubing), rupture of the main steam pipe, or station or plant blackout. In this case the vapor from the vapor generators are, in accordance with the teachings of the prior art, in part, vented into the atmosphere through a relief valve and in part by-passed around the turbine into the condenser if off-site power is available to drive the circulating pumps for the condenser. Since the turbine is not, during a major failure, delivering power, the condenser cooling may not be vailable. Excessive environmental radioactive emission is produced because of steam dump through the relief valve.
It is an object of this invention to overcome the above-described disadvantages of the prior-art nuclear-reactor plants and to provide such a plant in the use and operation of which environmental radioactive emissions shall be maintained within permissible limits.